Assessing mechanical deformations in two-winding transformer unit using reduced-order circuit model

• Terminal measurement based approach is used to make method non-invasive.
• Multi-winding transformer unit is represented by reduced-order ladder circuit.
• This circuit is used for identifying mechanical deformations in two-winding unit.
• Accuracy of the method in detecting deformations is found satisfactory.

Certain level of mechanical deformations in winding does not hamper the normal performance of power transformer. However, such incipient deformations if unattended could result in permanent failure of transformer. To this end, an approach is proposed to assess the severity of mechanical deformations in transformer winding. These deformations get reflected as changes in its high frequency behaviour. Hence, characterising the high frequency behaviour is essential. This requires building physically realisable ladder circuit corresponding to each winding. Thus, n-winding transformer is represented by n electrically and magnetically coupled ladder networks. In such scenario, the objective of fault diagnostics becomes very challenging. In this effort, realising the multi-winding unit by reduced-order ladder circuit model is explored. This approach essentially involves energising one winding at a time. Then, reduced-order ladder circuit of considered unit is synthesised from its measured driving-point impedance data. It is shown how these circuit models could be used for identifying mechanical deformations. To demonstrate capability of the method, two-winding model transformer is considered and deformations are introduced in its outer winding. Then, reduced-order circuit models are synthesised corresponding to healthy and faulty state of model transformer. The location of fault is identified by the changed parameter in the circuit. Further, the amount of change reveals the severity of introduced deformation. In all the cases, synthesised reduced-order circuit model agrees with that of model transformer with regard to driving-point impedance plot and results are found satisfactory.